1. Field of the Invention
This invention relates to a method of containerless crystallization of materials.
2. General Description of the Prior Art
It is known that polycrystalline fusable materials, such as semi-conductor materials of indium, antimony, germanium, or silicon, can be zone refined by vertically supporting an elongated body of the material in a chamber, spacing it from the inner wall of the chamber. The material is heated, establishing a molten zone which extends through the cross section of the body and over a small fraction of the length of the body. The zone is held in a stable position by forces of surface tension, causing the zone to traverse lengthwise at least a portion of the body by progressively melting along its length, and, finally, enabling one interface of the zone to progressively freeze. As presently practiced, the difficulty with this technique is that it is limited in application to the formation of molten zones having small cross-sectional areas. For example, if the molten zone cross-sectional area of a silicon rod is increased beyond about one centimeter, the zone becomes unstable. In order to solve this problem, various efforts have been made to support the molten zone by containerless techniques, principally by electromagnetic suspension. However, the difficulty remains of growth of crystals of a desired maximum size, it appearing that previous techniques have been unable to produce pure crystalline growth of a cross section greater than three inches per flow zone refined silicon.
Accordingly, it is the object of this invention to provide an improved method of crystal growth which enables the production of bulk crystalline materials of cross sections in excess of 50 inches, and typically on the order of 40 inches, depending on gravity levels and density of materials.